The transit of Venus, a rare astronomical event last witnessed in 1882, will be visible from Australia and around the world tomorrow.

The event starts at 5:07 UT on Tuesday 8 June (15:07 AEST).

The transit of Venus happens as Venus moves across the Sun's disc, similar to a solar eclipse. But Venus does not obscure the Sun because it is much further away than the Moon.

Instead Venus looks like a small, blurry dot moving across the Sun's disc.

After its first contact with the Sun, Venus will move across to the inside of the Sun's disc, with "second contact" occurring when Venus is fully within the Sun's disc. It will take six hours to move across the Sun before it makes "final contact", when the last point of the rim of Venus appears to touch the Sun.

But the Sun will set (at 6:53 UT and 16:53 AEST) before Australians can witness the end of the transit. The entire transit will be visible from Europe, Africa, Asia, and eastern parts of the U.S.

The transit should only be watched by using a telescope or binoculars to reflect the Sun's image on a blank piece of cardboard. Looking directly at the Sun with the naked eye or through telescopes or binoculars can cause blindness.

Transits of Venus are relatively rare, but two occur quite close together. The last transit was 122 years ago, but the next will be on 6 June 2012.

This is because the Earth, Venus and the Sun only line up at these times. Venus and Earth's orbital planes have a different orientation in space and the Earth has a slightly slower orbit than Venus.

Transits were important to astronomers historically as they used them to measure the distance from the Earth to the Sun.

One such journey to observe the transit in 1769 led Captain Cook to the east coast of Australia.

Observers will be able to see the unusual teardrop affect that led Cook to describe Venus atmosphere as a "dusky shade", NASA says.

This effect, called the "black drop", happens because of the thick atmosphere of Venus and the fact that the Sun's surface is "bubbly and not sharp", Ford said.

"It's like it's joined up by a little black bridge."

The phenomenon makes it difficult to establish the moment second contact starts.

"The surprising thing is that people like Cook and ... [and other] observers in Europe from the 1700s and 1800s were actually able to get very accurate results," Ford said of their attempts to calculate the distance from the Earth to the Sun.

If you averaged all the observations for the measurement of the distance from the Earth to the Sun taken historically the result is within 1% of what astronomers use today, said Ford.